Effect of water-binding ability of amorphous gel on the rheology of geopolymer fresh pastes with the different NaOH content at the early age

In this paper, composition of water, amorphous gel and rheology properties of fly ash-slag based geopolymer fresh pastes have been investigated by H-1 low-field NMR(LF-NMR), in-situ ATR FTIR and Brookfield DV3T rheometer under the different NaOH content. T-2 relaxation time of LF-NMR and gel characteristic peak of pastes was obtained to accurately study the influence of free water and gel on the fresh pastes. Results indicate the high transformation speed of free water and quicker formation speed of gel result to the more fluidity loss of geopolymer pastes. N-A-S-H and C-(A)-S-H gel were major reasons on the development of rheology properties. Higher water-binding ability of C-(A)-S-H gel may accelerate the transformation of free water to the gel water, which could increase the motion resistance of particles. It would result to the increasing of rheology peoperties and decreasing of fluidity of geopolymer fresh pastes. (C) 2020 Elsevier Ltd. All rights reserved.